[Cashtab] Deprecate xecApiBatchSize

Summary: Deprecating xecApiBatchSize in Ticker.js as it's an old BCH-API param and no longer in use since the chronikfication of Cashtab.

Test Plan:
grep -r xecApiBatchSize src/ and ensure no outputs
npm test

Reviewers: bytesofman, #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14119